Control systems for controlling the position of a hitch assembly coupled to a work vehicle, such as an agricultural tractor, are generally known and typically include position and draft feedback devices coupled to the hitch assembly, position and load command devices accessible from an operator station or cab, and a controller including a microprocessor for receiving and processing inputs from the feedback and command devices. Based upon these inputs, the controller typically outputs control signals to a positioning system including a hydraulic cylinder for raising and lowering the hitch in accordance with the operator-induced command signals. A hitch control system of this general type is described in U.S. Pat. No. 5,421,416, commonly owned with the present application and incorporated herein by reference.
Certain systems of the type described above include an upper limit input device that allows the operator to select a maximum upper or raised position for the hitch. The input device typically includes a knob coupled to a potentiometer that generates a signal recognized by the controller as the upper limit position. During manual or automatic control of the hitch assembly, such control systems typically do not permit movement of the hitch above the upper limit position.
Difficulties encountered in such control systems occur when, upon start-up of the tractor, the hitch is determined to be located in a position above the upper limit position or in a position that does not correspond with the position command device. Enabling automatic hitch movement under these conditions may result in unexpected, and possibly dangerous, movement of the hitch assembly and associated implement. The former condition may occur when the upper limit knob is adjusted (lowered) when the control system is off, such as after the vehicle is stopped and switched off. In this condition, the controller may be prevented from initiating automatic control of the hitch assembly in accordance with a predetermined automatic control routine until the hitch is captured and manually lowered to the upper limit position (e.g., using a manual position control knob or lever) or the upper limit is manually raised such that the detected hitch position falls within an allowable range. The latter condition may occur when the position command device is adjusted in either direction after the control system is shut off, or the hydraulics allow the hitch to physically move during this period. In this condition, the operator may be required to capture the hitch by adjusting the position command lever. Such approaches to these conditions burden the operator with the need to manually capture hitch position using the position command lever or upper limit device.
Accordingly, it would be advantageous to provide a simplified initialization sequence wherein an operator may capture the hitch and move it to an initialized position without being required to manually alter a position control or upper limit device. There is a need for an improved hitch control system that provides a simple initialization sequence which ensures that the hitch is positioned below an upper limit position prior to the occurrence of automatic control. There is also a need for an improved hitch control system that provides an initialization sequence which ensures that the hitch is positioned at the commanded position prior to the occurrence of automatic control.